You're already familiar with the inspector's test as a required component of a sprinkler system, but today we're diving into the true purpose and details behind this important aspect of a sprinkler system.

The purpose of the Inspector's Test can include: providing the ability to (1) test the sprinkler system's alarm/waterflow device, (2) test the opening of a dry-pipe or pre-action valve (for dry-pipe or pre-action systems systems, of course), (3) test the trip time from when the valve is opened to the arrival of water, where necessary, and (4) can aid in venting trapped air.

The inspector's test can be coupled as an air vent for a wet system or an auxiliary drain, although we'll explore those components in more detail separately.​

Figure 1: Example arrangement of an inspector's test and drain which is remote from the riser

​Discharge: Used to discharge water during the test or draining of the system. Discharge must:

route outside, to a drain capable of handling the flow, or another location where damage will not result (NFPA 13 2002 8.16.4.2.3, 2007-13 8.17.4.2.3, or 2016 8.17.4.1.3)

allow for at least 4 feet of exposed pipe between the wall penetration and the operating valve in an adjacent warm room in order to prevent freezing of the valve (NFPA 13 2002 Figure A.8.16.4.2(a), 2007-13 Figure A.8.17.4.2(a), or 2016 Figure A.8.17.4.1(a))

consider providing a 45 or 90-degree elbow at the exterior to avoid prolonged horizontal discharge

Drum Drip: Provided for dry or pre-action systems to collect condensate within the system for purging. At a minimum they must be:

accessible (NFPA 13 2007-16 8.16.2.5.3.1)

provided where the capacity of trapped sections of system piping is more than 5 gallons with a 2 inch x 12 inch condensate nipple (drum drip) or equivalent, or a device listed for this service (NFPA 13 2002 8.15.2.5.3.3, 2007 8.16.2.5.3.4, or 2010-16 8.16.2.5.3.5)

be provided with signage at the valve indicating the number and locations of low-point drains (NFPA 13 2007 8.16.2.5.3.6, 2010-16 8.16.2.5.3.7)

Orifice: The orifice (within a sight/site glass) simulates the flow of a single sprinkler in order to ensure that the sprinkler waterflow alarm will activate upon the flow of a single sprinkler. The orifice must:

be equal to the smallest orifice of any sprinkler installed on the system (NFPA 13 2002 8.16.4.1.1, 2007-16 8.17.4.1.1 for wet systems, 2002 8.16.4.2.1, 2007-16 8.17.4.2.1 for dry systems, 2010-13 8.17.4.3.3, or 2016 8.17.4.3.3 for pre-action systems)

when dry and pre-action systems have specific volumes (under 500 gallons without valve accelerator, or under 750 gallons with an accelerator), the orifice for an inspector's test can be equivalent to one sprinkler. Where the volume is greater and a 'trip-test' is used to time water delivery, then special provisions apply and a one-sprinkler orifice should not be used (NFPA 13 2013 8.17.4.3.4, 2016 8.17.4.2.4 for dry systems, 2013 8.17.4.4.6, 2016 8.17.4.3.6 for pre-action systems)

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Figure 2: Inspector's Test Connection to dry-pipe system when not used as an auxiliary drain

​Sight/Site Glass: typically provided where water discharge is not visible from the control valve (NFPA 13 2002 A.8.16.4.2, 2007-13 A.8.17.4.2, 2016 A.8.17.4.1). As a side note, I don't understand why Drive Thrus and Site Glasses are spelled the way they are, but I don't try to fight the system. Just know that common language often refers to these as 'site' glasses despite not actually referring to a large area of land.

Supply: The supply simply connects the most remote branchline from the riser to the inspector's test (for a remote inspector's test). It must:

When used for dry systems and not as an auxiliary drain, NFPA 13 Annex material suggest tapping the top of the branch line to minimize condensation of water in the drop to the test connection (NFPA 13 2002 Figure A.8.16.4.3, 2007-13 A.8.17.4.3, 2016 A.8.17.4.2)

are recommended to be no more than 7 feet above finished floor (NFPA 13 2002 A.8.16.4.2, 2007-13 A.8.17.4.2, 2016 A.8.17.4.1)

Wall Penetrations:

standard practice suggests properly sealing any exterior wall penetrations for insulative and water barrier needs, and potentially cleaning up any penetrations with escutcheons that offer a clean installed finish.

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Figure 3: Inspector's Test and Drain Located at a Floor Control Assembly

​When & Where Required: inspector's tests are required on each wet, dry, or pre-action sprinkler system:

wet systems: located anywhere downstream of the waterflow alarm, which could be at the sprinkler riser or remote from the riser. Some jurisdictions have requirements or preferences to locate the inspector's test remotely from the riser (NFPA 13 2007-13 8.17.4.2.4, 2016 8.17.4.1.4). Note that FM Global systems require wet system inspector's tests to be located remotely from the riser (FM Global 2-0 2.6.5)

dry and pre-action systems: located on the end of the most distant sprinkler pipe for each system in the upper story and equipped with accessible shutoff valve, with a plug not less than one-inch with at least one being brass or a nipple and cap (NFPA 13 2010-13 8.17.4.3.2 & .3, 2016 8.17.4.2.2 & .3 for dry, and 2010-13 8.17.4.4.4 & .5, 2016 8.17.4.3.4 & .5 for pre-action systems)

inspector's tests are not required for deluge systems, as they have open orifices (No NFPA 13 requirement, FM Global 2-0 2.6.5)

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